General Science Questions and Answers

Answer: B

LPG consists mainly of propane and butane, with some methane in the mixture.

These gases liquefy under modest pressure at ordinary temperature, so a great deal of fuel is stored in a small cylinder. Ethyl mercaptan is added to give the odourless mixture a warning smell.

Answer: B

Pearl is composed mainly of calcium carbonate with some magnesium carbonate, laid down by the oyster in thin concentric layers.

The carbonate is deposited as aragonite platelets bound by the protein conchiolin, and it is interference of light between these layers that produces a pearl's lustre.

Answer: D

To an astronaut, outer space appears black.

The sky is blue on earth because air molecules scatter sunlight; in the vacuum of space there is nothing to scatter it, so no light reaches the eye except directly from the sun, the stars and lit surfaces. The sun therefore shines against a black sky.

Answer: B

Carbon dioxide from fossil fuels is the main cause of the rise in average global temperature. Burning coal, oil and gas has raised its atmospheric concentration from about 280 ppm before the industrial era to over 420 ppm today.

Ozone depletion is a separate problem: it admits more ultraviolet radiation but does not by itself warm the lower atmosphere.

Answer: C

The speed of light in a medium remains unaltered by a change in the medium's temperature, to any appreciable degree.

It depends on the medium's refractive index, which is set by its optical density rather than by its temperature. In vacuum the speed is a fixed constant, 3 × 10⁸ m/s.

Answer: B

The oxygen released in photosynthesis comes from water, not from carbon dioxide.

In the light reaction water is split - photolysis - to supply electrons and hydrogen, and the oxygen is left over:

\[ \mathrm{2H_2O \rightarrow 4H^+ + 4e^- + O_2} \]

Experiments with the heavy isotope ¹⁸O in the 1940s proved it.

Answer: B

Balloons are filled with helium. It is much lighter than air, giving good lift, and unlike hydrogen it does not burn.

Hydrogen lifts slightly better but is dangerously flammable, as the Hindenburg disaster of 1937 demonstrated.

Answer: B

Sea water freezes at a slightly lower temperature than fresh water - about −1.9°C for water of normal salinity, against 0°C.

The dissolved salt lowers the freezing point, a colligative property that depends on the number of dissolved particles. As sea ice forms it excludes most of the salt, so the ice itself is nearly fresh.

Answer: A

The aorta is the largest blood vessel, about 2.5 to 3.5 cm across where it leaves the heart.

It carries oxygenated blood from the left ventricle and branches to supply the whole body. The largest vein is the vena cava; alveoli are air sacs in the lung, not vessels at all.

Answer: C

Soda water contains carbon dioxide, dissolved under pressure.

A little of it reacts with water to form carbonic acid, which gives the drink its sharp taste; the rest escapes as bubbles when the bottle is opened and the pressure drops.